Toss chopped carrots, onion, leek, Extra-Virgin Olive Oil (2 tablespoon) and Salt (1 teaspoon) until combined. Arrange on the baking sheet and bake until lightly browned and caramelized, about 30 minutes.
Transfer the vegetables to a large stockpot along with the Russet Potato (1 pound) and Vegetable Stock (8 cup). Bring to a boil.
Bring to a boil; turn the heat to medium and simmer, uncovered, until the potatoes are fork tender, about 20 minutes.
Off the heat, add the Yellow Miso Paste (1/3 cup) and Lemon (2 tablespoon).
Puree using a stand or immersion blender until smooth. Taste for seasoning and add more salt as necessary. (Depending on how salty your miso paste is, you might need more).
Transfer the soup to bowls or mugs and garnish with the Black Sesame Seeds (1 tablespoon), Pepitas (to taste) or Fresh Cilantro (to taste), if using. Serve and enjoy!